1. Field of the Invention
The present invention relates to a magnetic recording and reproducing system, and more specifically, to a high density magnetic recording operation, and still more particularly to a perpendicular magnetic recording operation.
2. Description of the Prior Art
A variety of systems have been designed so as to use a magnetic head for a magnetic recording and reproducing system according to the prior art. The magnetic heads according to the prior art can be classified in accordance with the output types into a magnetic flux differential type and a magnetic flux response type and in accordance with the the signal processing modes into an analog signal recording type and a digital signal recording type.
First of all, the magnetic flux differential type magnetic head can be represented by a ring type head. This head was invented in 1935 by E. Schiiller of Germany. Ever since, many improvements have been made so that the ring type head occupies a major role in the magnetic head field at present. Since the output voltage of the ring type head is expressed by dl/dt so that it is proportional to the changing rate of the magnetic flux with respect to time, a high output voltage can be obtained in the case of an analog type video tape recorder, in which the relative velocity between a magnetic recording medium and the magnetic head is high. In the case of a multi-track type PCM recorder, however, in which the relative velocity is low so that the changing rate of the magnetic flux with respect to time is low, the signal level approaches the level of noise such as the Barkhausen noises which are generated in the magnetic material of the magnetic head, thus making it difficult to reproduce the original signal. Therefore, the magnetic flux differential type magnetic head has its application limited to the use having at least a preset minimum changing rate of the magnetic flux with respect to time. In the application of the magnetic recording of a region wherein the changing rate of the magnetic flux with respect to time is low, the magnetic flux response type magnetic head is used, including a variable reluctance type head, a Hall element head and a magneto-resistance element head. These are heads for reproduction only, but they respond to the quantity of the magnetic flux so that they can reproduce magnetic recorded signals of low frequency containing a DC component. Therefore, the magnetic flux response type magnetic heads are suitable for application in the digital signal recording and reproducing apparatus, in which the reproducing rate is minimized by the use of the multiple tracks while having a low changing rate of magnetic flux with respect to time. However, the variable reluctance type head has a complex construction, and the Hall element head and the magneto-resistance element head require a bias current and a bias magnetic field, although their high frequency characteristics are excellent and their construction is simple, so that their S/N ratio is deteriorated by noise such as the Barkhausen noises. Because of the deteriorated S/N ratio, the magnetic flux response type magnetic head according to the prior art has its application limited to a low density system, even in the magnetic recording of the system having a low changing rate of the magnetic flux with respect to time, so that it is not suitable for the high density recording purpose which is being required from the market at present.
Now, the magnetic heads can be roughly classified in accordance with the signal processing modes into the digital signal recording system and the analog signal recording system, as has been described hereinbefore. The digital system has conventionally been used for industry, e.g., in a computer as well as widely used for home use, e.g., in a PCM tape recorder. In this meaning, it can be said that the significance of the digital magnetic recording and reproducing apparatus has been abruptly raised so that the developments for high density recording purposes are being accomplished in many companies.
Here, the conventional digital magnetic apparatus is different from the analog magnetic recording apparatus only in that the recording operation is effected while saturating the magnetization of the magnetic layer of the magnetic recording medium. It is not too much to say that the basic construction such as the reproducing or recording head follows the analog magnetic recording technique. In the reproducing circuit, on the other hand, it is the current practice that the continuously varying analog signals generated in the magnetic head are amplified by an analog signal and converted into digital signals. Although it is of the digital magnetic recording type, it is not greatly different from the magnetic recording mechanism of the analog magnetic recording in view of the output signal generation from the ring type magnetic head.
According to the conventional system, therefore, the advantages of the digital processing system are not sufficiently utilized so that it has been difficult to realize the higher density recording operation than the analog magnetic recording operation.
As a method suitable for the high density magnetic recording operation of the digital signals, on the other hand, a perpendicular magnetic recording system has been proposed so that the high density magnetic recording operation as high as 100 MBPI is realized.
In case, however, the high density recorded signals are to be reproduced, the record magnetizing signal of one wavelength is so fine as to require a remarkably highly sensitive magnetic head. However, the magnetic head having been realized has not been put into practice because it is short of sensitivity.
As has been described hereinbefore, the magnetic recording operation of the remarkably high density has been realized. Since, however, a detecting system of high sensitivity for reproducing the high density magnetic recorded signals is not realized, the advent of the magnetic detecting system having the higher sensitivity than that of the prior art has been awaited.
In case the higher density is to be realized, it becomes necessary to raise the track density. In this case, the tracking resorting to the magnetic head drive by an electromagnetic actuator becomes necessary. In this respect, as the weight of the magnetic head becomes the lower, the tracking becomes the easier so that the track density can be accordingly raised. Thus, a magnetic recording and reproducing system which has a lighter magnetic head without any reduction in the output voltage has been required.